Prof. Buff on the Eooperiment o/" Leidenfrost. 351 



small number. The current can thereby certainly to all ap- 

 pearance be interrupted ; whether this occurs or not, depends, 

 according to my experience, for a given liquid, on the de- 

 licacy of the galvanometer, on the strength of the electromo- 

 tive force, and finally on the size of the drop itself. The sphe- 

 roidal water behaves towards the hot surface as mercury towards 

 a \\-ire dipped into it, which is not wetted by the liquid metal. 

 In a memoir published several years ago [Annalen der Chemie 

 und Pharmacie, vol. Ixxvii. p. 1), I have communicated dif- 

 ferent modes of experiment, which are, moreover, very easily 

 devised, for the purpose of rendering visible the propagation of 

 an electric current through water in the spheroidal condition. 

 The most evident, however, as I learned afterwards, is the electric 

 glow first observed by Mackrell on thin metallic wires, when they 

 are used as electrodes of a very powerful electric circuit and im- 

 mersed in hot water. In the case of the negative pole, it might 

 be objected that during the continuance of the red heat it is 

 surrounded by a brush {spriihlicht) ; this, however, is not neces- 

 sarily the case with the positive wire, and when it is absent, the 

 wire exhibits at a red heat the phsenomenon of Leidenfrost per- 

 fectly. The current, and even the electrolytic decomposition, also 

 continue ; for when the positive electrode disperses no brush, the 

 gas developed upon it is always pure oxygen. The continuance 

 of the current in this and similar cases is perhaps not a certain 

 proof of the existence of direct contact ; for the layer of gas, or 

 ^'apour between the water and the red-hot surface, may at thia 

 high temperature assume a small degree of conductibility, I 

 am, however, only desirous of showing, that the extinction of 

 the current in other cases cannot be regarded as a proof of the 

 existence of an interval between the water and the surface by 

 which it is sustained. 



Indeed, the spheroidal condition of water exhibits in its moat 

 essential phEenomena sufficient evidence against tlie idea that 

 insulation and repulsion are necessary conditions of the sphe« 

 roidal state. Permit me to lay before you briefly those proQJ^ 

 which 1 regard as tiic most important. 



In a silver spoon coated with soot, water asserts the spheroidal 

 form at ordinary temperatures, exactly as when the spoon ia 

 raised to a high temperature. 



The drop which rolls upon the hot surface of a liquid, for 

 example a drop of aether upon water, bends the surface of the 

 liquid, as a mercury surface is bent by the pressure of a rod of 

 glass. 



Large drops assume an oscillatory motion, which often con- 

 tinue with remarkable regularity, and cause the formation of star- 

 shaped figures : without a partial contact of the water with the 



